Brown pine sign of blight

October 01, 2013|By Tim Johnson, Special to Tribune Newspapers

There is a pine tree in our front yard, though I am not sure what kind of pine tree it is. Many of the tree's needles are turning brown. Do you have any idea what could be causing this problem and what I can do to fix it? There was another pine tree in our yard that died last year.

— Limin Dove, Evanston

Dead, brown needles at the tips of pine branches, as in the photo you sent, indicate the presence of Diplodia tip blight.

Diplodia tip blight, previously known as Sphaeropsis tip blight, is a fungal disease of conifers, especially pines with needles in bunches of twos and threes, like your mugo pine. Another commonly grown conifer, Austrian pine (Pinus nigra), is one of the trees most susceptible to this blight.

The fungus affects trees most severely if they are stressed by site and cultural factors, such as growing in too much shade or in poor or compacted soils or by drought conditions. It generally does not affect trees that are under 15 years of age and does the most severe damage to trees that are more than 25 years old.

Diplodia will kill the current year's shoots and sometimes branches, disfiguring the tree, and can eventually kill it. The needles begin to die several weeks after infection. The symptoms often appear first on the bottom half of the tree and gradually move upward.

The fungus first affects the pines' new growth, or candles, when they are expanding in spring. They become stunted and turn yellow and then tan or brown. Droplets of resin may be seen on the dead shoots. The disease then moves on to kill lateral shoots and entire branches. Cankers, or abnormal growths in the bark, may form and cause branches to die.

Pines also can be damaged by the larvae of the pine shoot moth, which tunnel through the wood. If the damage is caused by this insect, either the larva itself or its tunnel will be found inside the dead shoot. To distinguish Diplodia tip blight from pine shoot moth damage, bend the dead tip. If it breaks and is hollow, the problem is probably pine moth larvae. If the dead shoot is flexible, the harm is probably from Diplodia.

Another sure sign of Diplodia is small, black fruiting bodies (pycnidia) that appear in fall at the base of needles or second-year cones. They can be seen with a hand lens. The Diplodia fungus overwinters in these fruiting bodies in infected shoots, bark and seed cones. Wind, rain and pruning will spread the fungus.

Sanitation is an important cultural step to help minimize this disease. Prune off the blighted shoots and twigs now and destroy them or discard them in landscape waste bags for pickup. Rake up all blighted needles, twigs and cones under the tree to reduce the amount of the overwintering fungus and also dispose of them in the landscape waste.

The fungal spores can be transported to healthy twigs while pruning, so prune only while the tree is dry and disinfect the pruning tools with Lysol disinfectant or 70 percent rubbing alcohol before every cut.

The open habit of your mugo pine suggests that it is growing in some degree of shade, which can stress a pine and make it more susceptible to Diplodia tip blight. Mugo pines grow best in full sun. Pruning back adjacent plants so more light reaches your pine may help its health.

There are fungicides that can be applied in spring to help your tree resist Diplodia tip blight. The chemical will have to be sprayed about three times at approximately 14-day intervals. The first application should be made as the buds are breaking, the second when the candles are half-grown, and the third when the candles are fully expanded.